Lithographic energy curable inks

ABSTRACT

An energy curable lithographic ink composition having an asymptotic relative viscosity of about 0.4 to about 1.5 and a water up-take number of at least about 30%. Also disclosed is a method of improving various rheological properties and increasing the water window of an energy curable lithographic ink by varying the composition of the ink in order to result in an asymptotic relative viscosity of about 0.4 to about 1.5 and a water up-take number of at least about 30%. A method of identifying and selecting an energy curable lithographic ink composition having optimal press performance is also disclosed.

FIELD OF THE INVENTION

[0001] This invention relates to an energy curable lithographic inkshaving improved or optimal press performance properties and larger waterwindows, and methods for making same.

BACKGROUND OF THE INVENTION

[0002] Ultra-violet light curable (UV) and electron beam energy curable(EB) lithographic inks are well established market products in theprinting ink or graphic arts market. Examples of energy curablelithographic inks are disclosed in U.S. Pat. No. 5,985,984 and U.S. Pat.No. 6,316,517, which is incorporated herein by reference. Their majorbenefits are good physical and, chemical resistance properties achievedimmediately after curing. Instantaneous cure of UV and EB inks allowsfor such uses as converting of folding cartons in-line without damaginga printed image (scratches, flaking off, etc.). However, conventionalUV/EB lithographic inks suffer from a number of lithographic printingdeficiencies such as narrow water window, poor emulsion quality whichresults in toning and scumming, and a tendency to pile on the offsetprinting blankets due to poor ink transfer and release which causesdefects in the printed image product, and adds cost to a need to changethe blankets.

[0003] Conventional oil based inks are also well established marketproducts in the lithographic printing market. However, conventional oilbased inks have numerous deficiencies as well. For example, the timeneeded to develop the polymerization qualities of a coated conventionallithographic film is excessive.

[0004] One approach has attempted to combine the UV/EB lithographic inkswith conventional oil based lithographic inks by applying UV/EBlithographic inks over conventional oil based inks. This approach hasnot been successful in that it typically results in a significantreduction in gloss and still requires a printed product be coatedoff-line after the conventional oil based ink is completely dry. Such anapproach normally requires a delay of up to 72 hours for theconventional oil based inks to dry completely before the UV/EB coatingcan be applied off-line, a problem known as “dry back”. This is due tothe fact that conventional oil based inks dry via a much sloweroxidation mechanism requiring multi-step drying and curing. All of thisresults in added print production expense and production timeconstraints. Thus, there is a need for a UV/EB lithographic ink thatmaintains good physical and chemical resistance properties immediatelyupon and after curing.

[0005] Unfortunately, it has always been a challenge to formulate energycurable lithographic inks using acrylate monomers and oligomers as“building blocks”. A number of publications and patents have suggestedthe use of conventional resins such as rosin esters and alkyds incombination with acrylated monomers and oligomers to improvelithographic press performance. However, practical implementation ofthese ideas has not been widely demonstrated due to serious difficultiesin producing stable mixtures of these materials so different in polarityand solubility. For example, UV lithographic inks have a limited wateror fountain solution tolerance, which is also referred to as “waterwindow.” Water window is defined as an ink's ability to sustain printdensity despite having an excessive amount of emulsified water. Inkswith narrow water window tend to cause many lithographic press problemssuch as poor ink transfer which results in low print density, toning,piling, scumming, and excessive dot gain. The, overall behavior oflithographic ink regarding these factors defines its lithographic pressperformance.

[0006] Even where a lithographic ink as described above is successfullyproduced, it does not have a long shelf life and is prone to easyseparation under severe printing press shear conditions, causing pilingon the rollers and blankets. The prior art does not teach how toformulate a mixture of conventional and UV/EB curable lithographic inkshaving optimal lithographic press performance. It also does not teachhow to effectively identify lithographic inks that offer optimal pressperformance from, for example, laboratory experiments.

[0007] Accordingly, there is a need to provide an energy curablelithographic ink composition having a long shelf life and optimallithographic performance, including but not limited to a wider waterwindow while still maintaining good lithographic performance on press,such as low dot gain, effective transfer of ink, effective ink trapping,good print contrast, good ink mileage and the absence of toning,scumming, picking, piling and dry back and other properties.

SUMMARY OF THE INVENTION

[0008] The present invention provides an energy curable lithographic inkhaving an asymptotic relative viscosity of about 0.4 to about 1.5 and awater up-take number of at least about 30%.

[0009] This invention also provides a method of increasing the waterwindow of an energy curable lithographic ink composition comprisingvarying said ink composition so as to result in an ink compositionhaving an asymptotic relative viscosity of about 0.4 to about 1.5 and awater up-take number of at least about 30%.

[0010] This invention further provides a method of improving at leastone press performance parameter selected from the group consisting ofink transfer, print contrast, dot gain, ink trapping, gloss and inkmileage for an energy curable lithographic ink composition so as toresult in an ink composition having an asymptotic relative viscosity ofabout 0.4 to about 1.5 and a water up-take number of at least about 30%.

[0011] This invention further provides a method of identifying an energycurable lithographic ink composition having optimal press performancecomprising selecting an ink composition having an asymptotic relativeviscosity of about 0.4 to about 1.5 and a water up-take number of atleast about 30%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows the relationship of relative viscosity versus shearstress for four different conventional energy curable lithographic inks.

[0013]FIG. 2 shows the relationship of relative viscosity versus shearstress for four different energy curable lithographic inks of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] It has now surprisingly been found that the water window andperformance press properties of an energy curable lithographic ink canbe significantly improved by formulating said ink based on associatedasymptotic relative viscosity (η_(r)) and water up-take WUT).

[0015] In general, the energy curable lithographic inks of the presentinvention are electron beam energy (EB) or ultra violet light (UV)curable inks containing rosin ester or hydrocarbon esters, natural orsynthetic oils and resins, and a mixture of reactive monomers andoligomers such as acrylates including difunctional epoxy acrylate or oilmodified tetrafunctional polyester acrylate. The energy curablelithographic inks of the present invention further contain alkyd andconventional resins used in non-energy curable lithographic inks such asrosin ester resins, maleic or phenolic modified rosin ester resin.Photoinitiators are further necessary for energy curable lithographicinks requiring UV curing, but they are not necessary for energy curablelithographic inks requiring EB curing.

[0016] The energy curable lithographic inks of the present inventionexhibit superior lithographic performance as defined above, regardlessof the exact percentages of the components of the composition. Forinstance, such inks exhibit a wide water window and far superiorlithographic press performance while offering rapid polymerization underUV or EB irradiation. The largest use improvement of the inks of thepresent invention lies in the ease of establishing and maintainingoperational press settings without continual modification during thepres run.

[0017] In establishing the criteria of the Theological performance ofthe inks of the present inventions, 10 parts of the ink is emulsifiedwith 1 part of water or any commercially available fountain solution onthe proper mixing equipment. Both neat and emulsified inks are thensubjected to a wide range of shear stress (flow experiment), typicallyfrom 0.01 to 10000 Pa using a rheometer. The geometry used to recordviscosity profiles is not restricted in any way. The measurements wereobtained using a cone-and-plate setting. As indicated above, theviscosity ratio between emulsified and neat inks(η_(r)=η_(emulsified)/η_(neat)) called asymptotic relative viscosity ofan energy curable lithographic ink should be between 0.4 and 1.5. Thebest performing energy curable lithographic inks should have a η_(r)between 0.7 and 1.1, and more preferably between 0.9 and 1.1. IN orderto optimize the lithographic press performance of the inks of thepresent invention, the η_(r) is recorded and if outside of the aboverange, components of the inks are modified so as to achieve the range.

[0018] The viscosity ratio is best obtained by extrapolation at infiniteshear stress, but is typically valid above 1000 Pa of stress or a stress10 times higher that the yield stress of the emulsified ink.

[0019] Additionally, the inks of the present invention exhibit a highwater up-take (WUT) which represents water capacity of the given ink andis determined by mixing together 100 g of ink with 100 ml of water orfountain solution until no more water is emulsified by the ink. Thepercent of water (volume by weight) incorporated into the ink isrecorded as a WUT percentage. It has been determined that the WUTpercentage should not be lower than 30%, and can be as high as 80%, inorder to achieve superior performance on press.

[0020] In order to achieve superior press performance, the inks of thepresent invention are formulated such that both the η_(r) ratio and WUTpercentage are within the above ranges and thus the components of theinks of the present invention may require modification in order toachieve said ranges. Failure to meet both the η_(r) of between about 0.4to about 1.1 and the WUT of at least 30% leads to a number oflithographic printing complications, including poor ink transfer,toning, piling, scumming and other printing problems.

[0021] Ink Performance Properties

[0022] It has been found that certain lithographic press performanceproperties must be maintained (by a UV/EB lithographic ink, in order forit to effectively print. For example, in optimal lithographic printingthe water window should be wide, dot gain should be low, print densityshould be high, ink transfer and trapping should be good, print contrastshould be good, there should be no piling or picking, the emulsionquality must be high enough so as to avoid toning and scumming, mileageof the ink should be high, and the frequent need for blanket wash shouldbe low.

[0023] “Dot gain” is defined as an increase in dot size as a result oftransferring image from the printing plate on the substrate. “Trapping”is defined as the overlap of one printing ink over a-previously printedink. “Picking” is defined as the pulling of tiny pieces of the papersubstrate by an ink with too high a tack. “Piling” is defined as thebuild up of ink on the offset blanket. “Toning” is defined as thecontamination of the non-image area of the print with ink. “Scumming” isdefined as the contamination of fountain solution with ink particles.“Ink mileage” is defined as the number of prints that can be producedwith the same amount of ink. The frequency between the need for blanketwashes is measured by the number of impressions between said requiredblanket washes, where the washes are required due to dried ink on thepress blanket. The frequency of blanket washes should optimally be lowwhile the number of impressions between blanket washes should be high.

[0024] It has been found that the press performance of an energy curablelithographic ink can be predicted and thus the press performancecontrolled based on the inks asymptotic relative viscosity and WUT.

[0025] Rheology Criteria

[0026] Ink having the lithographic press performance propertiesdescribed above preferably should have an optimal asymptotic relativeviscosity. The energy curable lithographic ink of the present inventionis produced by first emulsifying 10 parts of distilled water or fountainsolution in 100 parts of ink by high-speed mixing using Cowles blades at1000 rpm at room temperature for one minute. This amount is notrestrictive and the same results may be obtained at any water level inthe emulsified ink between 5% and the maximum the ink can take up,determined by the water up-take test. Minimal heating is noticed duringthe emulsification step.

[0027] Viscosities are recorded on a stress-controlled rheometer, modelAR1000 from TA Instruments using a 2 cm 0.5° cone. The stress is rampedin the interval 0.01-10000 Pa and viscosity is recorded versus stress.For each stress value, the relative viscosity η_(r) is calculated bydividing the viscosity of the emulsified ink by the viscosity of theneat ink.

[0028]FIG. 1 shows typical curves for conventional inks and FIG. 2 showstypical curves for the inks of the present invention (see description ofinks below) obtained using this test. The curve of the inks of thepresent invention always tend to have an asymptotic value atsufficiently high stress. The global shape of the curve may varydepending on the interactions taking place in the sample between allphases present. Accurate calculation of the relative viscosity requiresthat a large enough portion of the curve be recorded at high stress.Typically, this is true above 1000 Pa.

[0029] Any method-using shear can be-used to obtain the asymptotic valueof the viscosity including but not limited to capillary viscometers,cone-and-plate, concentric cylinder on any type of viscometer orrheometer (stress- and rate-controlled), and others presently known inthe art.

[0030] Water Window

[0031] Inks having the optimal lithographic press performance propertiesdescribed above should have a water window of at least 30%. The waterwindow of inks of the present invention are determined on a two colorsheet-fed Miehle press by first supplying the minimum amount of water(fountain solution) required to clean up a non-image area of thelithographic plate and achieve target print density (typically 1.00 foryellow, 1.35 for red, 1.4 for blue and 1.65 for black) . Once density isachieved, additional water is supplied gradually by opening watercontrol keys in the fountain solution unit. After each incrementalincrease in water supply is completed, about 200 sheets are printed andprint density is measured. This increase of water supply continues untilprint density drops significantly, at least 0.1 in print density(5-10%). The spread between initial and final water key settingsrepresents water window or the range of water tolerance of the testedink.

[0032] The following examples illustrate the invention. The examples usemultiple colors (yellow, magenta, cyan, black and a blended blue) of theinks of the present invention and of comparison examples to show theoptimal performance properties maintained by the ink of the presentinvention having a WUT and rheological criteria of the presentinvention.

EXAMPLE 1

[0033] UV or EB curable inks of the present invention were prepared bymixing a pigment with liquid mixture of resins, oligomers monomers,photoinitiators in case of UV curing (no photoinitiator for EB curableinks). Each ink composition was then ground on 3 roll mill until properpigment particle size distribution was achieved. After grinding wascompleted, the ink was ready for printing.

[0034] Table 1 below shows the composition of energy curablelithographic inks (Example 1A-1D Inks) that meet the WUT and h_(r)criteria simultaneously. The difference between the four example inks isonly the type of pigment added to each ink composition. TABLE 1 ExampleExample Example Example 1-A 1-B 1-C 1-D Materials (Yellow) (Magenta)(Black) (Cyan) Inhibitor 2.0 2.0 2.0 2.0 Hard Resin (Rosin 22.0 22.022.0 24.0 or hydrocarbon in Monomer DITMPTA) Oligomer 17.0 17.0 16.018.0 (tetrafunctional polyester acrylate) Oligomer 7.0 14.0 12.0 13.0(difunctional epoxy acrylate) Monomer (DITMPTA, 29.5 17.5 14.5 14.5TMPTA) Alkyd 5.0 5.0 5.0 5.0 Photoinitiator 3.0 4.0 7.0 4.0 Talc 3.0 3.02.0 3.0 Wax 0.5 0.5 0.5 0.5 Pigment 11.0 15.0 19.0 16.0 100.0 100.0100.0 100.0

COMPARATIVE EXAMPLE 2

[0035] Conventional energy curable lithographic inks (Conventional Inks2A-2D) were prepared by mixing a pigment with liquid mixture of resins,oligomers monomers, photoinitiators in case of UV curing (nophotoinitiator for EB curable inks). Each ink composition was thenground on 3 roll mill until proper pigment to particle size distributionwas achieved. After grinding was completed, the ink was ready forprinting.

[0036] Table 2 below shows the composition of conventional energycurable lithographic inks that do not meet the WUT and h_(r) criteriasimultaneously. The difference between the four conventional inks isonly the type of pigment added to each ink composition. TABLE 2 Conven.Conven. Conven. Conven. 2-A 2-B 2-C 2-D Materials (Yellow) (Magenta)(Black) (Cyan) Inhibitor 1.0 1.0 2.0 1.0 Hard Resin — — 20.4 —(Polyurethane Urea as described in U.S. Pat. No. 5,985,984) in monomerDifunctional epoxy 23.6 16.0 24.5 24.8 acrylate (oil modified)Tetrafunctional 8.3 10.2 10.2 — polyester Flush color (hard 54.7 62.1 —54.7 resin solution, oil modified epoxy acrylate, monomer and pigment)described in U.S. Pat. No. 5,985,989 Photoinitiator 6.8 7.1 10.2 7.0 Wax1.0 1.0 1.0 1.0 Talc 3.6 2.6 3.0 3.0 Fumed Silica 1.0 — 1.0 2.0 Monomer(TPGDA, E- — — 9.4 6.5 TMPTA, GPTA) Pigment — — 18.3 — 100.0 100.0 100.0100.0

EXAMPLE 3

[0037] The Example 1A-1D Inks and Conventional 2A-2D Inks were testedfor WUT and-viscosity ratio (at infinite stress) with the followingresults. TABLE 3 Ink WUT η_(r) Example 1-A (Yellow Pigment) 30 0.63Conventional 2-A (Yellow Pigment) 26 0.16 Example 1-B (Magenta Pigment)40 1.10 Conventional 2-B (Magenta Pigment) 40 0.21 Example 1-C (BlackPigment) 36 0.45 Conventional 2-C (Black Pigment) 26 0.11 Example 1-D(Cyan Pigment) 38 0.51 Conventional 2-D(Cyan Pigment) 28 0.12

[0038] As indicated in Table 3 above, the conventional ink compositionsdo not meet requirements for both criteria simultaneously, while theExample 1A-1D Inks show very high water acceptance combined with minimalreduction in viscosity. Batch-to-batch variations may affect thesenumbers by about 10%.

EXAMPLE 4

[0039] Example 1A-1D Inks, having the water up-take and η_(r) rangesdescribed above, were tested for lithographic printing properties. Theinks were applied onto a paper board substrate via a Hamilton press andaverage measurements for density (measured by a Densitometer) and dotgain were observed over a period of several hours. The following averageresults for this time period are set forth in Table 4below: TABLE 4Example Example Example Example 1-A 1-B 1-C 1-D (Yellow) (Magenta)(Cyan) (Black) Density .96 1.37 1.44 1.7 Dot gain 13% 21% 16% 13%

[0040] Example 1A-1D Inks exhibited good lithographic printingqualities. The dot gain was low and density was near target for eachpigment.

EXAMPLE 5

[0041] Using Example 1A-1C inks and Conventional 2A-2C Inks, a test wasperformed to measure performance attributes in the increase of printmileage as indicated by the cut of ink keys and overall water balancebased on ability of the inks to print with reduced amount of water. Thecontrol inks and experimental inks were applied onto a paper board. Theresults are set forth below. TABLE 5 Cut of ink Water Motor Scumming Inkkeys Speed Density Example 1-A (Yellow 8 12 0.02 Pigment) Conventional2-A — 20 0.078 (Yellow Pigment) Example 1-B (Magenta 4 12 0.07 Pigment)Conventional 2-B — 24 0.057 (Magenta Pigment) Example 1-C (Black 20  400.02 Pigment) Conventional 2-C — 48 0.065 (Black Pigment)

[0042] Example 1A-1C Inks had a better water balance which led toreduced scumming. Example 1A-1C Inks were observed to have a dramaticdecrease in scumming (over 90%). Thus, the inks of the present inventionhaving a WUT of at least 30% and qr of between about 0.4 to about 1.5had better lithographic printing qualities, as set-forth in Table 6below. TABLE 6 Reduction in Reduction in Ink Water Speed ScummingExample 1-A (Yellow Pigment) 40% 91% versus Conventional 2-A (YellowPigment) Example 1-B (Magenta Pigment) 33% 96% versus Conventional 2-B(Magenta Pigment) Example 1-C (Black 17% 97% Pigment)versus Conventional2-C (Black Pigment)

[0043] Using the method as set forth in Example 1, an energy curable inkhaving a WUT of at least 30% and qr of between about 0.4 to about 1.5was produced with the following components): TABLE 7 Inhibitor 2.0 HardResin (Rosin 16.0 or hydrocarbon in Monomer DITMPTA) Oligomer 21.0(tetrafunctional polyester acrylate) Oligomer 8.0 (difunctional epoxy)Monomer (DITMPTA, 24.7 TMPTA) Alkyd 5.0 Photoinitiator 4.0 Talc 3.0 Wax.5 Pigment (Red) 15.8 100.0

[0044] The energy curable ink (Example 6 Ink) was then tested on a paperboard substrate applied via a 8 unit Hamilton off-line press with waterbased coating station and interstation UV lamps. Compared to aconventional energy curable ink (SunCure 2000® UV lithographic offsetink manufactured by Sun Chemical, Inc., Ft. Lee, N.J. and outside of therange of WUT of at least 30% and qr of between about 0.4 to about 1.5and referred to as 10 “Conventional Ink of Example 6”), Example 6 Inkhad a water setting which was reduced 30 points (from 50 with thestandard to 20 with Example 6 Ink). Further, the density of Example,6Ink was on target at 1.46. In addition, Example 6 Ink trapped better(red over yellow) than the conventional ink in that visually it had moreuniform coverage of the red over yellow.

EXAMPLE 7

[0045] The same inks from Example 6 were then tested for lithographicproperties of mileage and average density. Both inks were separatelyloaded into empty Hamilton web off-set presses and the amount of paperboard cartons and pounds of ink used to produced said cartons over aperiod of about five hours were recorded. The following results are setforth below: TABLE 8 Conventional Ink Example 6 from Example 6 Number ofcartons produced 109,800 145,200 Pounds of ink used 23.5 34 Cartons perpound of ink 4,672.34 4,270.58 Average density* 154 133 Ink versus waterratio** 45/40 49/42

[0046] Example 6 Ink had a higher viscosity than that of ConventionalInk 6. Example 6 Ink was observed to have a 6% increase in mileageversus the control ink, which would be equivalent to 11% increase basedon the 14% higher density of Example 6 Ink.

EXAMPLE 8

[0047] The same inks from Example 6 were then tested for lithographicproperties of water settings, print density and dot gain. Both inks wereseparately loaded into empty Hamilton presses and measurements for watersettings, print density (measure by a Densitometer) and dot gain wereobserved over a period of a few hours. The following average results forthis time period are set forth in Table 9 below: TABLE 9 ConventionalInk from Example 6 Example 6 Water settings 20 50 Print density 1.461.28 Dot gain 23 25

[0048] Example 6 Ink had a lower water setting and therefore printedscum free with a lower amount of fountain solution as 5 compared withConventional Ink from Example 6. Example 6 Ink had a higher dot gain(about 10%) while also maintaining a higher print density.

EXAMPLE 9

[0049] Using the method as set forth in Example 1, an energy curable inkwithin the range of WUT of at least 30% and η_(r) of between about 0.4to about 1.5 was produced with the following components: TABLE 10Inhibitor 2.0 Hard Resin (Rosin 14.0 or hydrocarbon in Monomer DITMPTA)Oligomer 20.6 (tetrafunctional polyester acrylate) Oligomer 7.5(difunctional epoxy) Monomer (DITMPTA, 29.2 TMPTA) Alkyd 4.7Photoinitiator 3.7 Talc 2.3 Wax .5 Pigment (Red) 15.0 Clay .5 100.0

[0050] Compared to a conventional energy curable ink (SunCure 2000®—Conventional Ink 6 from Example 6), Example 9 Ink had lower tackwithout causing any scumming problems. Example 9 Ink was tested on apaper board substrate applied via a Planeta UV Sheetfed Press and it wasobserved that compared to a standard maximum 2,000 of sheets betweenblanket washes, Example 9 Ink went a maximum of 8,000 sheets to 20,000sheets between blanket washes. Example 9 Ink was observed to have astable viscosity and less scumming, in addition to better pressstability.

EXAMPLE 10

[0051] Using the method as set forth in Example 1, an energy curableblended blue ink, having a WUT of at least 30% and η_(r) of betweenabout 0.4 to about 1.5, was produced by combining FLK5481618 (an energycurable lithographic ink of the present invention manufactured by SunChemical, Inc. of Ft. Lee, N.J.) in an amount of 57% of the total ink,FLK6481619 (an energy curable lithographic ink of the present inventionmanufactured by Sun Chemical, Inc. of Ft. Lee, N.J.) in an amount of32.5% of the total ink and FLKSV9481621 (an energy curable lithographicink of the present invention manufactured by Sun Chemical, Inc. of Ft,Lee, N.J.) in an amount of 1% of the total ink'and Dimptaq, a monomer(manufactured by both Sartomer, Inc. and Hognis, Inc.). The ink was thencompared to a conventional energy curable ink (SunCure 2000®—Conventional Ink from Example 6) by applying both inks on a paper boardsubstrate using a Planeta UV Sheetfed Press. The results of the test areset forth in Table 11 below: TABLE 11 Conventional Ink from Example 10Example 6 Tack at 1200 rpm 13 10 Dot gain 23% 39%

[0052] It was observed that the Example 10 ink had a better originalviscosity, higher tack without picking, and achieved good dot gain. Incomparison, the conventional ink from Example 6 had a lower tack so asto eliminate picking which developed and in turn had an unacceptablyhigh dot gain.

[0053] The foregoing examples are not intended to be limiting. Otherexamples and applications will be apparent to persons of skill in theart. The invention has also been described in terms of preferredembodiments, thereof, but is more broadly applicable as will beunderstood by those skilled in the art. The scope of the invention isestablished, by the following set of claims.

What is claimed is:
 1. An energy curable lithographic ink compositioncomprising an asymptotic relative viscosity of about 0.4 to about 1.5and a water up-take number of at least about 30%.
 2. The energy curablelithographic ink composition of claim 1, wherein said asymptoticrelative viscosity is about 0.9 to about 1.1.
 3. The energy curablelithographic ink composition of claim 1, wherein said asymptoticrelative viscosity is about 0.7 to about 1.1.
 4. The energy-curablelithographic ink composition of claim 1, wherein said water up-takenumber is at least about 40%.
 5. The energy curable lithographic inkcomposition of claim 1, wherein said water up-take number is at leastabout 35%.
 6. The energy curable lithographic ink composition of claim 1curable by electron beam energy.
 7. The energy curable lithographic inkcomposition of claim 1 curable by ultra-violet light.
 8. The energycurable lithographic ink composition of claim 1 curable by a combinationof electron beam energy and ultra-violet light.
 9. The energy curablelithographic ink composition of claim 1 further comprising an acrylateand a rosin ester resin.
 10. The energy curable lithographic inkcomposition of claim 9, wherein said acrylate is selected from the groupconsisting of difunctional epoxy acrylate, oil modified tetrafunctionalpolyester acrylate, or combination thereof.
 11. The energy curablelithographic ink composition of claim 9, wherein said rosin ester resinis selected from the group consisting of maleic modified rosin esterrein, phenolic modified rosin ester resin, or combination thereof. 12.The energy curable lithographic ink composition of claim 1, furthercomprising an alkyd.
 13. A method of increasing the water window of anenergy curable lithographic ink composition comprising varying said inkcomposition so as to result in an ink composition having an asymptoticrelative viscosity of about 0.4 to about 1.5 and a water up-take numberof at least about 30%.
 14. The method of claim 13, wherein said inkcomposition is varied by adding to said ink composition an alkyd and/ora rosin ester resin.
 15. The method of claim 14', wherein said rosinester resin is selected from the group consisting of maleic modifiedrosin ester resin, phenolic modified rosin ester resin, or combinationthereof.
 16. The method of claim 13, wherein said asymptotic relativeviscosity is about 0.9 to about 1.1.
 17. The method of claim 13, whereinsaid asymptotic relative viscosity is about 0.7 to about 1.1.
 18. Themethod of claim 13, wherein said water up-take number is at least about40%.
 19. The method of claim 13, wherein said water up-take number is atleast about 35%.
 20. The method of claim 13, wherein said energy curablelithographic ink is curable by electron beam energy.
 21. The method ofclaim 13 wherein said energy curable lithographic ink is curable byultra-violet light.
 22. The method of claim 13 wherein said energycurable lithographic ink is curable by a combination of electron beamenergy and ultra-violet light.
 23. A method of improving at least onepress performance parameter selected from the group consisting of inktransfer, print contrast, dot gain, ink trapping, gloss and ink mileagefor an energy curable lithographic ink composition, comprising varyingthe ink composition so as to result in an ink composition having anasymptotic relative viscosity of about 0.4 to about 1.5 and a waterup-take number of at least about 30%.
 24. A method of identifying anenergy curable lithographic ink having optimal press performancecomprising selecting an ink having an asymptotic relative viscosity anda water up-take number.
 25. The method of claim 24 wherein saidasymptotic relative viscosity is between about 0.4 to about 1.5.
 26. Themethod of claim 24 wherein said water up-take number is at least about30%.